In 2018, NASA satellite images of penguin guano sent researchers to Antarctica's Danger Islands, where they found more than 1.5 million Adélie penguins

In December 2015, a small team of scientists arrived on a cluster of icy islands near the tip of the Antarctic Peninsula. They were not chasing headlines; they were just following a pink stain they had seen in satellite pictures. It turned out to be penguin droppings, and it led to one of Antarctica's biggest wildlife finds in decades. A study published in the journal Scientific Reports, led by biologist Alex Borowicz and his team at Stony Brook University, confirmed the find. The remote Danger Islands were home to more than 1.5 million Adélie penguins. Nobody had fully counted them before.

The Adélie penguins are small and black-and-white seabirds. They live and breed only in Antarctica. Previously, scientists thought that the population of these birds across the continent was on the decline. The Danger Islands changed that picture. They are a chain of nine small rocky islands located north of the peninsula's tip. The islands are surrounded by sea ice most of the time, which makes them inaccessible by boat. This isolation could be the reason the colony was not found for so long.

How penguin droppings pointed the way


Adélie penguins nest in the same rocky spots every year. Over time, their droppings pile up and leave behind large stains on the ground. The stains are large enough to be detected in satellite images. The idea was first proposed by NASA scientist Mathew Schwaller back in 1984. Since then, the concept has been widely adopted. NASA's Earth Observatory explains the details of the method. The color and structure of guano stains allow scientists to make an estimate of the colony's size without setting foot on the island.

Scientists from Stony Brook University, including ecologist Heather Lynch, used this technique to identify the Danger Islands as worth further investigation. The pink spots could easily be identified in satellite imagery. They knew they had stumbled upon something significant.

Counting penguins by hand, drone, and eye

Satellite images can't count birds one by one. So in December 2015 the team traveled to the islands to test their theory in person. They walked the cold rocky slopes. They counted the penguins by hand, nest by nest. They also flew a modified commercial quadcopter drone above the islands. It took aerial photographs of the colonies. The computers then scanned those images. This helped track birds that may have been invisible to the human eye.

The team counted 751,527 breeding pairs. That number is higher than that for the whole Antarctic Peninsula. It includes the third and fourth largest populations of Adélie penguins ever recorded. It was possible to miss some birds with ground counts only. Drone images filled in the gaps. Together, they helped the researchers get a much more accurate count of the birds.

Why this colony held on while others struggled

There is yet another reason why the discovery became important. Adélie penguins have been drastically decreasing in number in other areas of the Antarctic Peninsula. This is particularly true for the west side of the peninsula. In 2016, an analysis carried out by oceanographer Megan Cimino and her associates tried to understand the reasons behind the decline. The study found that the warming of sea surface temperatures led to a decrease in the size of Adélie penguin colonies. Researchers also predicted further decreases due to the continued warming of some areas of the peninsula.

The Danger Islands are located on the eastern part of the peninsula. The environment there has remained relatively stable. The research team's paper points to this as one of the reasons that can explain why the colony did not suffer from the same declines. Scientists do not yet fully understand why there is such a difference in the numbers of penguins on the east and west sides. It may be a matter of sea ice patterns or food supply or some combination of the two.

What the discovery means going forward

This discovery provided conservationists with an important piece of information. They got an accurate baseline number. With the accurate count of the penguins in Danger Islands, the conservationists would be able to monitor whether their population is increasing or decreasing in the coming years. The colony size was a strong argument for protecting the region. There have been suggestions from marine biologists regarding the creation of zones to protect the region near the Antarctic Peninsula. Such zones would restrict any form of activity in the region, such as fishing. Ecologist Heather Lynch said in a statement that this information will be helpful in making decisions. For example, it can help plan marine protected areas and manage the adjacent krill fishery. Krill are small shrimp-like animals that serve as food for penguins.

For now, the Danger Islands stand as a reminder. There are still some mysteries left about Antarctica. Today’s satellites continue to observe the continent from outer space. However, it took a combination of good old-fashioned on-the-ground science and advanced technology to find more than a million penguins hiding in plain sight.